Reproductive success in mammals is dependent on the pituitary-gonadal reproductive axis. Follicle-stimulating hormone (FSH) is a critical component of the reproductive axis. This hormone has important effects on both the development and differentiation of the testis. FSH elicits its biological effects through the FSH receptor (FSHR), which is expressed exclusively in Sertoli cells in the testis and granulosa cells in the ovary. The cell-specific expression of the FSHR suggests that mechanisms specific to the gonads are involved in its transcriptional activation. We hypothesize that the mechanism regulating FSHR gene expression in Sertoli cells will involve a unique set of transcription factors binding to the promoter region of the FSHR gene. The unique nature of FSHR expression in Sertoli cells, suggest these factors may be globally important for a host of transcriptional events occurring during gene activation in Sertoli cells. The specific aims in this proposal are designed to identify important control regions of the FSHR gene in vivo by in vivo genomic footprinting using ligation-mediated (LM)-PCR and to identify and characterize the protein(s) that bind an important FSHR promoter element, the E-box, using DNA oligonucleotide affinity chromatography.